Field of the Invention
The present invention relates to a display device and, more particularly, to a display device which can provide optimal luminance and visibility to viewers by considering a viewing environment, a viewing distance and image characteristics in an associated manner and a method for driving the same.
Discussion of the Related Art
Distinguished from IT/mobile devices or TVs, outdoor display devices are used in various surrounding environments and user environments and need to display images with high luminance in the range of 1500 to 2000 nit. For example, outdoor display devices are exposed to very high ambient illumination to very low ambient illumination and to very high temperature to very low temperature since the outdoor display devices are installed in extreme environments of day and night. Furthermore, a recent outdoor display device has been combined with IoT (Internet of things) and developed to a form attached to a touchscreen, such as a personal device. Accordingly, outdoor display devices are used in environments having various viewing distances including a short distance to a very long distance between the outdoor display devices and users.
Therefore, it is necessary to control picture quality of outdoor display devices according to surrounding environments and user environments. However, when methods for controlling picture quality of display devices of the related art are applied to outdoor display devices, the following problems are generated.
For example, a liquid crystal display (LCD) of the related art uses a method of controlling luminance according to illumination or temperature, a method of controlling luminance according to viewing distance or a method of correcting gamma according to average luminance of an input image as a picture quality control technique.
However, when the LCD controls luminance according to illumination only, luminance deterioration characteristics of the LCD according to temperature are not reflected in luminance control and high luminance causes glare when a viewing distance is very short, and thus luminance suitable for viewers cannot be provided. When the LCD controls luminance according to viewing distance only, visibility of an output image decreases extremely due to low luminance when ambient illumination is high. In addition, when the LCD controls luminance according to illumination or viewing distance only, image characteristics are not reflected in luminance control and thus gray-level banding may occur in an output image when the image is output with low luminance, resulting in image distortion. When only gamma correction is controlled according to average luminance of an input image, visibility decreases since the surrounding environment and viewing distance are not considered, and the luminance of an image having a highlighted part on a black background is deteriorated due to low average luminance, resulting in picture quality decrease.
As described above, the LCD picture quality control techniques of the related art are not suitable for outdoor display devices since the techniques do not consider viewing environments, viewing distances and image characteristics in an associated manner and thus luminance unsuitable for viewers may be output or image distortion may occur.
Furthermore, the aforementioned problems may be generated in various display devices including an organic light-emitting diode (OLED) display as well as the LCD and even in display devices for various purposes in addition to outdoor display devices. Accordingly, the present invention is not limited to LCD or outdoor display devices.